Hydrolysis of titanium salt solutions



Patented Oct. 25, 1938 v UNITED STATES HYDR-OLYSIS OF TITANIUM- TIONS SALT I s'o-LU- Benjamin Wilson Allan, Baltimore, Md., assignor to American Zirconium-Corporation, Baltimore, Md., a corporation of Maryland No Drawing. Application April 4, 1936,

Serial No. vznes-- This invention relates to titanium dioxide and has particular reference to a new and novel method of producing pigmentary titanium dioxide by hydrolysis of titanium salt solutions. More particularly it refers to a new and novel method of accelerating the hydrolysis of such solutions,

whereby improved tinting strength is obtainable with substantially the same amounts of seeding,

agent as used by the prior art. In particular, it contemplates improvement in tinting strength by the addition to the solution of small quantities of seeding agent at various stages of the hydrolysis, instead of at the beginning.

Titanium oxide is one of the most popularof the pigments used in the paint industry, because of its chemical inertness and its exceptionally ood covering power. It is ordinarily madefrom rutile (a native titanium oxide mineral) or from ilmenite (an iron titanate mineral). The tita- '15, nium is put into solution in any desired manner,

.35, tion of titanium oxide is to start with the mineral ilmenite and attack the mineral with hot concentrated sulfuric acid, generally using sufiicient sulfuric acid to form normal salts with all of the iron and titanium present. The attack mass is then leached with water or with weak sulfuric acid, recovered later in the process, theresulting solution containing titanium and iron sulfates with some free acid. In some cases it is advantageous to use smaller percentages of sulfuric acid, in which case the titanium is present as a compound between 'IiOSO4 andTi(SO 4)2. The amount of sulfuric acid in the solution is expressed as factor of acidity (F. A.), TiOSO4 representing zero factor of acidity and Ti(SO4)2 rep- 49 resenting 100% F. A. The sulfate solutions are then reduced so that the iron is present in the ferrous condition, so that iron will not precipitate upon hydrolysis of the solutions. Suspended matter is ordinarily removed by filtration or other form of clarification and the solution is then ready for hydrolysis.

Some solutions are hydrolizable by mere boiling, but solutions made by treatment of ilmenite with acid in the manner above described, produce 50 rather poor yields of titanium oxide on simple 4 Claims. (01. a-zb) boiling. This difference in solutions I attribute to the, form' of the titanium oxide before solution. Where solutions are madefromortho titanic acid or where ortho titanic'acid has been formed and redissolved, hydrolysis is a'simple process; where the titanium oxide is dissolved from other modifications, the process-of hydrolysis becomes morev diflicult. The difference is probably due to the fact that ortho titanic. acid goes into colloidal rather than into. true solution.

Various investigators have suggested different methods of producing solutionswhich are readily hydrolizable, in every caseyadding to the solution some titanium oxide which has been precipi-' tated in the form of ortho titanic acid, or which goes into colloidal rather than true solution. In" some cases the precipitate is, formed, in the solutiongand later dissolved, thehydro-lysis being one continuous operation. In other cases a titanium oxide seeding agent-is prepared on the outside and thereafter added tothe solution.

Typical seeding agents prepared in solution are disclosed in the Blumenfeld Reissue Patents 17,429, 17,430 and 18,854. In this typeof seeding, the seeding agent is prepared in-situ by diifusing solutions of different concentration into one an-Y other; and theseeding agentv is ofnecessity all presentatthe beginning of the hydrolysis. r

The -other methodofseeding, the addition of seeding agents prepared separately, is well illustrated byi the Mecklenburg Reissue Patent 18,790, -by the Rhodes Patent 1,922,328 and by the Richter Patent. 1,947,226; Such an agent,,and my preferred seeding agent, is described in my co-pending application Serial #731,998, filed June 22, 19351 Patent 204.0,823; this seeding agent comprises a dry .gel of titanium dioxide, prepared by neutralizinga titanium salt solution with an alkaline material. v

. These lastmentioned seeding agents are added conventionallyto the solution to be hydrolized,

at the boiling point.' Good yields are generally obtainable by these methods, together with good tintingstrength. I H I have discoveredthatif the seeding agent be added to'the hydrolysis solutionat various stages infthe precipitation,theresultant precipitate is mucheasier toprecipitate, and the calcined pigment has in general, much better color and a definitely increased tinting strength ofthe order of 5 to 10%. Iattribute thisimprovement. in properties to the improved'phy'si'calstructure of the precipitate; I believe that when a seeding agent is added, it is gradually occluded with the hydrolytically precipitating titanium oxide, so that after a time, the hydrolysis solution produces a precipitate somewhat different in structure than the first precipitate; and the further addition of seeding agent changes the character of the precipitate back to that obtained originally, this precipitate being of such a physical nature as to calcine to a better tinting strength pigment. The improvement of color is probably due both 'to the physical structure, and to the fact that probably less impurities are occluded.

As a typical example of my invention, I pre= pared a titanium sulfate solution which, when ready for hydrolysis, had the following analysis:

T102 grams :per liter; 198 Fe -4. dO-

Total H2804 do 5 42 Free acid do I32 Active acid do 374 Factor of acidity per cent- I 54.5

This solution was heated to boiling, and 2% of a titanium oxide gel containing 10% T10: prepared as described in my =co"-'pending application Serial #731,998, filed June 22, 1934, Patent 2,040,823 were added. Boiling was continued for '6 hours; the pigment was filtered, washed 'and calcined at 900 C. after adding potassium carbonate as -a conditioning "agent. The resultant *pi'gme'nt was a slightly creamy white pigment, with very high tinting strength, numerically-set at 94 on an arbitrary scam in use in "our laboratory. The yield was 95%.

The same soliition was then hydroli'z'ed, adding A% "of the gel "at the boiling point, each hour for 3 hours, and at 5 hours. After 8 hours, the pigment was finished exactly as above. A 94.5% yield of pigment was obtai'ned'; it was much whiter and brighter than the firstpigment, and had a tint of98. While this 4% increase an tint seems rather smau, it is "or defihiteimfioi tance, particularly where "c'onipos'ite pigments are to be made, where "the high'e'i tihtin'g Strength base permits or a cheaper-com osite, or a better product for the same mane". 'rne (sharps-incipal difference lay in the fact that the filtration rate was 25% faster "in trie seccsnaease.

The-'aboy'e results were obtafri'dihthe eaters tory. On plant see-1e operations, siib'stahtiiillir greater differences e'obtairiable. eirarii'ple, usingjsbliitidiis very similar to the 'a ilfiii e, orest hydrolyses were niade i-n the one case adsmegrv, of-gel 'at th'e boning 'oina'inieie other-adding the -g e l in increments of at he v y iri'ti'i als. The color 'o'ft'he pigment obtained oi'r'i'the dela'yed seed was far superior; th'e tih-t was 93 against '85; the oijl absorption was Somewhat higher; the pigment "was somewhat softer; and the precipitate filtered and settled about faster. The yields were almost ide'iitical.

As another example of 'iny invention, I pre pared 10 liters of a titanium siilfai-te solemn of the followingcomposition TiOz grams per liter; +1 96 360 -per cent; 50 The solutionwa's split -into "two'parts, and "each heated to'boilin'g simultaneously. Aseed suspension was prepared following the disclosure of the Mecklenburg Reissue Patent 18,790; and 2.5% of the seed suspension was added to each of the two boiling solutions. In the first case, the entire quantity was added at the boiling point; in the second, the seed was added in increments, as follows: 7

4% at boiling point: at the end of the first, second, third and fourth hours; 4% at the end of five hours. Where all the seed was added at once, 93.5% precipitation was obtained in three hours, increasing only to 94.5% in eight hours. The delayed seeding resulted in a 73% yield in three hours, and a 93.5% yield in eight hours. 7 The Tpi'giheht properties of the precipitate, seeded at the boiling point, were considerably poorer than those obtained by delaying. the seed- 'i-"ng. The tint was increased from 83 to 90, the color was considerably brighter, and the filtration rate was increased by at least 50%. I V

The total amount of seeding'agent has, within limits, a slight effect on the yields; buttlieiraot manner 'of addition has little *efie'b't, except that somewhat better-yields are obtainable by adding a slight increment or seeding agent toward the very end of the hydrolysis. 4 The use of retirements f S ee'di'n'g agent a'ddd during'the course or hydrolysis improves pigment properties oye'r the sii'igle addition of seeding agent at the beginning, not only for the seeds shown, but for the seediag agents disclosed in the Rhodes and Richter patents' asoye eitee. -I believe the phenomenon tbbe 'generic roran s'eediifg agents hs'dih the hydrolytic precipitation -'of titanium salt soliitiohs." I V I claim: a 1. In thepro'ces's of hydroly'tically precipitating titanium 'oiiide "from a hydro'lizable titanium salt solution which comprises heatin'gthe solution in thepres'en'ce of a seeding agent, the improvement which com-prises adding a portion -orily of the seeding agent to thehydrolys'i's solution at the boiling "point, thereafter continuing the heating of the solution until a substantial amount *0? hydrolysis iseifected and then adizliiig andther portion of the "seeding ageiitand thereafter-continuing the heating. r

2. In the process of hydrolyti'cally precipitating titanium o'ifide' rrom a diydr'cSIiZable titaiiiin'n salt solution which comprises heating the sblutior'i 1h the pres'enoeo'f a- 'seeding a geht, the improvement which comprise heating the tit'a-iiium salt 'sdlution at the'boiliiig pointthereo'f'in the prese'iiiie 6f a p'oi ti'on only ofthe-seeding agemjumil a sims'tantial amount of hydrolysis is eif'ected and then adding another portion offthe seeding ag"e'r'it and thereafter 'contiriiiin'g tl'iehatiii'g.

' a 3. In the proc's'sof liydrolyti'allyprcip'itatini titanium oxide from "a hydrol-iiable *titahiiiin smfat'e solution which bbrhpris'es' hatfri'gi'the sdlu tion in the presence off a seedingagent, the linproveiner'it which boriipris's' heating the titanium sulfate solution at the boiling p'oiiit't'her'e'of in "the presence of 'a portion any "of t helseedihg agent until a substantial amount 'ojf hydrolysis, "is efiecte'dand 'th' adding ahbtlierpdrtioh 6f the seediirg agerit ai'i'd ther'ea'ftr cb'fitiiiiiin'g the heat 

